Power supplies for electroluminescent lamps or panels typically include inverters having a regulated or fixed output, or a tuned circuit for a single lamp or panel size. The tuned inverters can only be tuned for single lamp sizes. In other words, the tuned circuitry requires that the inverter be matched to the size or surface area of the panel. Such tuned inverters have some compensation for change in lamp load due to aging in that the drive signal current, voltage and frequency will rise slowly over time as the lamp ages in order to maintain power to the lamp. There are several drawbacks with prior tuned inverters. First, the inverters cannot power a range of lamp sizes. Hundreds of distinct inverters are necessary to be inventoried in order to cover the entire range of lamp sizes which is both inefficient and uneconomical. Second, these tuned inverters provide only modest compensation for change in the lamp load due to aging. Such compensation only marginally improves half life over regulated or constant or fixed output inverters. Third, permitting the frequency to drift as compensation for lamp aging results in an undesirable color shift emanating from the lamp and may result in a shorter operating life.
Inverters that have regulated or fixed outputs can power a range of lamp sizes, but have no compensation to the changing load of the lamp as it ages over its operating life. Therefore, the brightness half-life values of such fixed output inverters are relatively short. An additional drawback with both fixed output and tuned inverters is that they have been known to provide only DC voltage inputs, but not AC voltage inputs, such as at 115 VAC or 230 VAC. For large lamps, AC voltage inputs are the only practical means of operation.
There has been a recent demand for brighter electroluminescent lamps even if such brighter lamps should result in a shorter total operating life. Furthermore, the market is demanding an electroluminescent power supply which operates over a range of lamp sizes without the above-mentioned disadvantages.
Accordingly, it is an object of the present invention to provide a power supply which operates over a range of lamp sizes while providing voltage compensation due to aging of the lamp.
It is another object of the present invention to provide a power supply for an electroluminescent lamp which better maintains the brightness of the lamp over its operating life.
It is yet another object of the present invention to provide a longer operating half life of the electroluminescent lamp.
It is yet another object of the present invention to provide a power supply having temperature compensation with limits for outdoor temperatures through voltage limiting in order to prevent runaway voltages.
It is still another object of the present invention to provide a power supply which prevents a color shift in the lamp load due to aging.
The above and other objects and advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.